Arsenic in Soils Affected by Mining: Microscopic Studies vs. Sequential Chemical Extraction

Area of Science:

• Environmental Science
• Geochemistry
• Mineralogy

Background:

• Arsenic (As) contamination in soils poses environmental and health risks.
• Understanding As mobility in mine-affected soils is crucial for risk assessment and remediation.

Purpose of the Study:

• To investigate the influence of mineralogy, geochemistry, and texture of mine wastes on arsenic mobility.
• To compare sequential chemical extraction with microscopic techniques for As speciation in soils.

Main Methods:

• Soil sampling from three inactive arsenic-bearing mines.
• Sequential chemical extraction to determine As partitioning.
• Microscopic analysis including Scanning Electron Microscopy-Energy Dispersive Spectroscopy (SEM-EDS) and High Resolution Transmission Electron Microscopy (HR-TEM).

Main Results:

• Arsenic in soils is predominantly associated with the residual fraction, indicating mechanical dispersion as the primary pollution pathway.
• Microscopic techniques revealed sequential extraction methods overestimate the role of amorphous manganese oxy-hydroxides and organic matter in As retention.
• Sequential extraction underestimates As adsorption onto clay particle surfaces.

Conclusions:

• Mechanical dispersion is a key factor in arsenic soil pollution from mine wastes.
• Advanced microscopic techniques provide a more accurate assessment of arsenic speciation and mobility mechanisms than traditional extraction methods.
• Re-evaluation of arsenic retention mechanisms in mine-affected soils is necessary, considering adsorption onto clay minerals.